Gorilla WebSocket Uses Cryptographically Weak PRNG for WebSocket Mask Key

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

gorilla/websocket used math/rand (cryptographically weak pseudo-random number generator) to generate WebSocket frame mask keys prior to commit d67f4185. WebSocket masking keys MUST be unpredictable to prevent frame content injection attacks. math/rand produces deterministic output when seeded with a known value, enabling an attacker to predict or recover mask keys and inject content into WebSocket connections. Type: Use of Cryptographically Weak Pseudo-Random Number Generator Fix: Replaced math/rand with crypto/rand (commit d67f4185, released in v1.5.3) Credit: bounty-hunter v6.0 silent-fix detection

Published by the source

24 Aug 2026, 21:00 UTC

Last modified by the source

26 Aug 2026, 16:27 UTC

Source last checked

26 Oct 2026, 15:28 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w67g-5rqw-f597

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6278

4. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w67g-5rqw-f597

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# Patch Next advisory brief: GHSA-w67g-5rqw-f597

Advisory: Gorilla WebSocket Uses Cryptographically Weak PRNG for WebSocket Mask Key
IDs: GHSA-w67g-5rqw-f597
Record: https://patchnext.com/advisories/ghsa-w67g-5rqw-f597 (revision 4, source checked 26 Oct 2026, 15:28 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/gorilla/websocket 1.5.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/gorilla/websocket: affected < 1.5.3; fixed in 1.5.3

## Suggested inspection (read-only)
- Go github.com/gorilla/websocket: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/gorilla/websocket.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-w67g-5rqw-f597 (OSV record GHSA-w67g-5rqw-f597 lists affected ranges: Go github.com/gorilla/websocket >=0 <1.5.3 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6278 (OSV record GO-2026-6278 lists affected ranges: Go github.com/gorilla/websocket >=0 <1.5.3 (fixed))
- Verified: https://github.com/advisories/GHSA-w67g-5rqw-f597 (GitHub-reviewed advisory GHSA-w67g-5rqw-f597 lists affected ranges: Go github.com/gorilla/websocket >=0 <1.5.3)

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